Question

What property of hydrogen is observed in the following experiments.
When black cupric oxide is heated in a stream of hydrogen, reddish
colour is obtained.

Answer 1

Dear Student

Black CuO reacts with hydrogen to give reddish coloured copper metal and water.
CuO + H₂ $\to$Cu + H₂O - Redox reaction
In this reaction, the reducing nature of hydrogen is observed. Hydrogen here reduces Cu(II) in CuO and gets oxidized to H⁺ in the water itself.

Regards